1. Technical Field
The present invention relates to an electric direct-acting actuator for converting the rotary motion of an electric motor to a linear motion to linearly drive an object to be driven, and an electric brake device which uses an electric direct-acting actuator to press a braking member against a member to be braked.
2. Background Art
Electric direct-acting actuators for converting the rotary motion of an electric motor to a linear motion to linearly drive an object to be driven typically include ball-screw mechanisms or ball-ramp mechanisms for such motion conversion. Also, in order to obtain a large linear driving force with a small-capacity electric motor, such actuators typically include a gear speed reducer such as a planetary gear speed reducer (as disclosed e.g. in JP patent publication 6-327190A (FIGS. 1 and 5)).
On the other hand, although many of today's vehicle brake devices are of the hydraulic type, electric brake devices are gathering attention now because they can perform sophisticated brake control functions that are used in today's vehicles, such as ABS (antilock brake system) without the need for complicated hydraulic circuits, and thus can be designed compactly. In this type of electric brake device, an electric motor is actuated based on a signal indicating that the brake pedal has been depressed, and the braking member is pressed against a member to be braked by means of the above-described type of electric direct-acting actuator, which is mounted in a caliper body (as disclosed e.g. in JP patent publication 2003-343620A (FIG. 1)).
Because such electric brake devices are mounted under springs of a vehicle, it is desired that such brake devices operate stably even if vibrations transmitted from the road surface are applied thereto and can be designed compactly.